The Melbourne teen bashed at a party on Saturday night has had his condition downgraded from critical to serious.

Jaiden, 15, remains in intensive care at The Royal Children’s Hospital, suffering bleeding on his brain.

Police have released few details in the hunt for his attacker.

They say they are looking for a male in his late teens to early 20s, who was wearing a hoodie at the time of the attack and possibly has blond hair.

Police were called to the party on Saturday night, believed to have been at a community hall, on the corner of Station Street and Pine Road in the eastern Melbourne suburb of Bayswater after reports of numerous gatecrashers and fights.

They found about 100 party-goers and other teenagers spilling on to the nearby streets and witnesses told police the Carrum Downs boy had been knocked to the ground and struck his head on the footpath after being punched.

Jaiden was treated by paramedics at the scene and was then collected by his mother, Karyn.

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On the way home, he began having seizures and Karyn rushed him to the Angliss Hospital. He was later transferred to the Royal Children’s Hospital where he was placed into an induced coma.

Yesterday, his mother said he was destined to become a professional soccer player.

The 15-year-old was due to fly to Italy in September to trial for a place in the Italian Soccer Management Schools program, which offers advanced training from professional coaching staff to promising young players from across the world.

He had also been pursuing local options through his school, Flinders Christian Community College as well as playing with the Bentleigh Greens Soccer Club’s junior side. The Greens are a semi-professional side based in Cheltenham that play in the National Premier Leagues Victoria.

His mother said Jaiden had been excited about the upcoming trial and had dreamt of playing professionally.

“He absolutely had not only the ability but the desire,” his mother said.

Police were called to the party. (Facebook) ()

Jaiden had been attending a social gathering organised by a schoolmate – not a 16th birthday party as initially reported - when the attack occurred.

“The group that have had these sorts of functions before… things have never go to the point that it has got to,” Karyn said.

Jaiden’s condition is listed as critical and he’s still in an induced coma, his brother Anthony said.

"He's the nicest kid you could meet in the world," he said.

His family have pleaded for the attacker to come forward.

"Be honest, please. You might not realise that the outcome of your action is what it is ... but you need to know and young people need to know this is not on," his mother said.

The Facebook page of the party. (Supplied: Facebook) (Facebook)

Police broke up several fights after arriving at the scene of the bashing but said the crowd returned and continued fighting.

Detective Rick Rittinger said Jaiden was hit without warning.

"It was a case of the offender running past and stopping the victim and continuing running. There was no altercation, nothing said," he told reporters.

More than 600 people are believed to have attended the party. (Facebook) ()

The party’s Facebook page claims 623 attended, with the original organiser setting out "there will be rules", including: "no fighting, no weapons allowed, trouble makers will be kicked out, plz respect the venue” as well as warning partygoers that strict security would be in force on the venue’s door.

Experienced event organiser Daniel Tusia, of Applause Entertainment, said the party sounded like a "recipe for disaster".

He said it was vital to provide adequate security, structure and parental supervision when dealing with teenage parties.

"It’s important when you’re dealing with kids’ parties – and they are kids, they’re not adults just yet – to provide that level of structure,” the party planner said.

"If they’ve just hired a hall, it’s just a recipe for disaster, it’s just asking for it.

"You’ve got more than 100 kids turning up, it’s not enough just to hire a DJ and let them go - you've got to ask where were the parents, did they even know about the party?"

Mr Tusia, who has organised and run parties ranging from corporate functions through to teenaged birthday parties, said an "increasing" number of teenagers were seeking to organise their parties – sometimes without parental knowledge or approval.

A string of similar incidents involving huge numbers of gatecrashers turning up at parties advertised via social media has prompted many police officers to discourage people from promoting events.

The NSW Police Force-run Mynite.com.au urges parents to organise professional security at the door or at least have responsible friends on hand to refuse entry to gatecrashers.

Police are looking for a male with blue jeans, a hoodie and possibly blond hair. aged in his late-teens to early 20s.

The incident comes just days after the Victorian government announced it would introduce mandatory 10-year jail terms for perpetrators of one-punch attacks which result in a death.

Police are appealing for anyone who may have information about the incident to contact Crime Stoppers on 1800 333 000 or via www.crimestoppers.com.au.